// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// Filter performs filtering on data streams. Sample usage:
//
//   IStream* pre_filter_source;
//   ...
//   std::unique_ptr<Filter> filter = Filter::Factory(filter_type, size);
//   int pre_filter_data_len = filter->stream_buffer_size();
//   pre_filter_source->read(filter->stream_buffer(), pre_filter_data_len);
//
//   filter->FlushStreamBuffer(pre_filter_data_len);
//
//   char post_filter_buf[kBufferSize];
//   int post_filter_data_len = kBufferSize;
//   filter->ReadFilteredData(post_filter_buf, &post_filter_data_len);
//
// To filter a data stream, the caller first gets filter's stream_buffer_
// through its accessor and fills in stream_buffer_ with pre-filter data, next
// calls FlushStreamBuffer to notify Filter, then calls ReadFilteredData
// repeatedly to get all the filtered data. After all data have been filtered
// and read out, the caller may fill in stream_buffer_ again. This
// WriteBuffer-Flush-Read cycle is repeated until reaching the end of data
// stream.
//
// A return of FILTER_OK from ReadData() means that more data is
// available to a future ReadData() call and data may not be written
// into stream_buffer(). A return of FILTER_NEED_MORE_DATA from ReadData()
// indicates that no data will be forthcoming from the filter until
// it receives more input data, and that the buffer at
// stream_buffer() may be written to.
//
// The filter being complete (no more data to provide) may be indicated
// by either returning FILTER_DONE or by returning FILTER_OK and indicating
// zero bytes output; consumers understand both those signals. Consumers
// are responsible for not calling ReadData() on a filter after one of these
// signals have been returned. Note that some filters may never signal that
// they are done (e.g. a pass-through filter will always
// say FILTER_NEED_MORE_DATA), so the consumer will also need to
// recognize the state of |no_more_input_data_available &&
// filter->stream_data_len() == 0| as FILTER_DONE.
//
// The lifetime of a Filter instance is completely controlled by its caller.

#ifndef NET_FILTER_FILTER_H__
#define NET_FILTER_FILTER_H__

#include <stdint.h>

#include <memory>
#include <string>
#include <vector>

#include "base/gtest_prod_util.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/time/time.h"
#include "net/base/net_export.h"
#include "net/base/sdch_manager.h"

class GURL;

namespace net {

class BoundNetLog;
class IOBuffer;
class URLRequestContext;

//------------------------------------------------------------------------------
// Define an interface class that allows access to contextual information
// supplied by the owner of this filter. In the case where there are a chain of
// filters, there is only one owner of all the chained filters, and that context
// is passed to the constructor of all those filters. To be clear, the context
// does NOT reflect the position in a chain, or the fact that there are prior
// or later filters in a chain.
//
// TODO(rdsmith): FilterContext is a grab-bag of methods which may or may
// not be relevant for any particular filter, and it's getting worse over
// time. In addition, it only supports two filters, SDCH and gzip.
// It would make more sense to implement FilterContext as a
// base::SupportsUserData structure to which filter-specific information
// could be added by whatever the ultimate consumer of the filter chain is,
// and a particular filter (if included) could access that information.
class NET_EXPORT_PRIVATE FilterContext {
public:
    // Enum to control what histograms are emitted near end-of-life of this
    // instance.
    enum StatisticSelector {
        SDCH_DECODE,
        SDCH_PASSTHROUGH,
        SDCH_EXPERIMENT_DECODE,
        SDCH_EXPERIMENT_HOLDBACK,
    };

    virtual ~FilterContext();

    // What mime type was specified in the header for this data?
    // Only makes senses for some types of contexts, and returns false
    // when not applicable.
    virtual bool GetMimeType(std::string* mime_type) const = 0;

    // What URL was used to access this data?
    // Return false if gurl is not present.
    virtual bool GetURL(GURL* gurl) const = 0;

    // When was this data requested from a server?
    virtual base::Time GetRequestTime() const = 0;

    // Is data supplied from cache, or fresh across the net?
    virtual bool IsCachedContent() const = 0;

    // Was this data flagged as a response to a request with an SDCH dictionary?
    virtual SdchManager::DictionarySet* SdchDictionariesAdvertised() const = 0;

    // How many bytes were read from the net or cache so far (and potentially
    // pushed into a filter for processing)?
    virtual int64_t GetByteReadCount() const = 0;

    // What response code was received with the associated network transaction?
    // For example: 200 is ok.  4xx are error codes. etc.
    virtual int GetResponseCode() const = 0;

    // The URLRequestContext associated with the request.
    virtual const URLRequestContext* GetURLRequestContext() const = 0;

    // The following method forces the context to emit a specific set of
    // statistics as selected by the argument.
    virtual void RecordPacketStats(StatisticSelector statistic) const = 0;

    // The BoundNetLog of the associated request.
    virtual const BoundNetLog& GetNetLog() const = 0;
};

//------------------------------------------------------------------------------
class NET_EXPORT_PRIVATE Filter {
public:
    // Return values of function ReadFilteredData.
    enum FilterStatus {
        // Read filtered data successfully
        FILTER_OK,
        // Read filtered data successfully, and the data in the buffer has been
        // consumed by the filter, but more data is needed in order to continue
        // filtering. At this point, the caller is free to reuse the filter
        // buffer to provide more data.
        FILTER_NEED_MORE_DATA,
        // Read filtered data successfully, and filter reaches the end of the data
        // stream.
        FILTER_DONE,
        // There is an error during filtering.
        FILTER_ERROR
    };

    // Specifies type of filters that can be created.  Do not change the values
    // of this enum; it is preserved in a histogram.
    enum FilterType {
        FILTER_TYPE_BROTLI,
        FILTER_TYPE_DEFLATE,
        FILTER_TYPE_GZIP,
        FILTER_TYPE_GZIP_HELPING_SDCH, // Gzip possible, but pass through allowed.
        FILTER_TYPE_SDCH,
        FILTER_TYPE_SDCH_POSSIBLE, // Sdch possible, but pass through allowed.
        FILTER_TYPE_UNSUPPORTED,

        FILTER_TYPE_MAX
    };

    virtual ~Filter();

    // Creates a Filter object.
    // Parameters: Filter_types specifies the type of filter created;
    // filter_context allows filters to acquire additional details needed for
    // construction and operation, such as a specification of requisite input
    // buffer size.
    // If success, the function returns the pointer to the Filter object created.
    // If failed or a filter is not needed, the function returns NULL.
    //
    // Note: filter_types is an array of filter types (content encoding types as
    // provided in an HTTP header), which will be chained together serially to do
    // successive filtering of data. The types in the vector are ordered based on
    // encoding order, and the filters are chained to operate in the reverse
    // (decoding) order. For example, types[0] = FILTER_TYPE_SDCH,
    // types[1] = FILTER_TYPE_GZIP will cause data to first be gunzip filtered,
    // and the resulting output from that filter will be sdch decoded.
    static std::unique_ptr<Filter> Factory(
        const std::vector<FilterType>& filter_types,
        const FilterContext& filter_context);

    // A simpler version of Factory() which creates a single, unchained
    // Filter of type FILTER_TYPE_GZIP, or NULL if the filter could not be
    // initialized.
    static std::unique_ptr<Filter> GZipFactory();

    // External call to obtain data from this filter chain. If ther is no
    // next_filter_, then it obtains data from this specific filter.
    FilterStatus ReadData(char* dest_buffer, int* dest_len);

    // Returns a pointer to the stream_buffer_.
    IOBuffer* stream_buffer() const { return stream_buffer_.get(); }

    // Returns the maximum size of stream_buffer_ in number of chars.
    int stream_buffer_size() const { return stream_buffer_size_; }

    // Returns the total number of chars remaining in stream_buffer_ to be
    // filtered.
    //
    // If the function returns 0 then all data has been filtered, and the caller
    // is safe to copy new data into stream_buffer_.
    int stream_data_len() const { return stream_data_len_; }

    // Flushes stream_buffer_ for next round of filtering. After copying data to
    // stream_buffer_, the caller should call this function to notify Filter to
    // start filtering. Then after this function is called, the caller can get
    // post-filtered data using ReadFilteredData. The caller must not write to
    // stream_buffer_ and call this function again before stream_buffer_ is
    // emptied out by ReadFilteredData.
    //
    // The input stream_data_len is the length (in number of chars) of valid
    // data in stream_buffer_. It can not be greater than stream_buffer_size_.
    // The function returns true if success, and false otherwise.
    bool FlushStreamBuffer(int stream_data_len);

    // Translate the text of a filter name (from Content-Encoding header) into a
    // FilterType.
    static FilterType ConvertEncodingToType(const std::string& filter_type);

    // Given a array of encoding_types, try to do some error recovery adjustment
    // to the list. This includes handling known bugs in the Apache server (where
    // redundant gzip encoding is specified), as well as issues regarding SDCH
    // encoding, where various proxies and anti-virus products modify or strip the
    // encodings. These fixups require context, which includes whether this
    // response was made to an SDCH request (i.e., an available dictionary was
    // advertised in the GET), as well as the mime type of the content.
    static void FixupEncodingTypes(const FilterContext& filter_context,
        std::vector<FilterType>* encoding_types);

    // Returns a string describing the FilterTypes implemented by this filter.
    std::string OrderedFilterList() const;

    FilterType type() const { return type_id_; }

protected:
    friend class BrotliUnitTest;
    friend class GZipUnitTest;
    friend class SdchFilterChainingTest;
    FRIEND_TEST_ALL_PREFIXES(FilterTest, ThreeFilterChain);

    explicit Filter(FilterType type_id);

    // Filters the data stored in stream_buffer_ and writes the output into the
    // dest_buffer passed in.
    //
    // Upon entry, *dest_len is the total size (in number of chars) of the
    // destination buffer. Upon exit, *dest_len is the actual number of chars
    // written into the destination buffer.
    //
    // This function will fail if there is no pre-filter data in the
    // stream_buffer_. On the other hand, *dest_len can be 0 upon successful
    // return. For example, a decoding filter may process some pre-filter data
    // but not produce output yet.
    virtual FilterStatus ReadFilteredData(char* dest_buffer, int* dest_len) = 0;

    // Copy pre-filter data directly to destination buffer without decoding.
    FilterStatus CopyOut(char* dest_buffer, int* dest_len);

    FilterStatus last_status() const { return last_status_; }

    // Buffer to hold the data to be filtered (the input queue).
    scoped_refptr<IOBuffer> stream_buffer_;

    // Maximum size of stream_buffer_ in number of chars.
    int stream_buffer_size_;

    // Pointer to the next data in stream_buffer_ to be filtered.
    char* next_stream_data_;

    // Total number of remaining chars in stream_buffer_ to be filtered.
    int stream_data_len_;

private:
    // Allocates and initializes stream_buffer_ and stream_buffer_size_.
    void InitBuffer(int size);

    // A factory helper for creating filters for within a chain of potentially
    // multiple encodings. If a chain of filters is created, then this may be
    // called multiple times during the filter creation process. In most simple
    // cases, this is only called once. Returns NULL and cleans up (deleting
    // filter_list) if a new filter can't be constructed.
    static std::unique_ptr<Filter> PrependNewFilter(
        FilterType type_id,
        const FilterContext& filter_context,
        int buffer_size,
        std::unique_ptr<Filter> filter_list);

    // Helper methods for PrependNewFilter. If initialization is successful,
    // they return a fully initialized Filter. Otherwise, return NULL.
    static std::unique_ptr<Filter> InitBrotliFilter(FilterType type_id,
        int buffer_size);
    static std::unique_ptr<Filter> InitGZipFilter(FilterType type_id,
        int buffer_size);
    static std::unique_ptr<Filter> InitSdchFilter(
        FilterType type_id,
        const FilterContext& filter_context,
        int buffer_size);

    // Helper function to empty our output into the next filter's input.
    void PushDataIntoNextFilter();

    // Constructs a filter with an internal buffer of the given size.
    // Only meant to be called by unit tests that need to control the buffer size.
    static std::unique_ptr<Filter> FactoryForTests(
        const std::vector<FilterType>& filter_types,
        const FilterContext& filter_context,
        int buffer_size);

    // An optional filter to process output from this filter.
    std::unique_ptr<Filter> next_filter_;

    // Remember what status or local filter last returned so we can better handle
    // chained filters.
    FilterStatus last_status_;

    // The filter type this filter was constructed from.
    FilterType type_id_;

    DISALLOW_COPY_AND_ASSIGN(Filter);
};

} // namespace net

#endif // NET_FILTER_FILTER_H__
